Dinosaur bones reveal evidence against cold blooded creatures

Modern mammals show similar growth patterns in their bones.

Who can get enough of dinosaurs? We’re curious about what color they were, how fast they moved, and whether they could really spit venom at Newman from Seinfeld. One of the most fundamental questions is whether they were cold-blooded or warm-blooded. Just because some of them looked like fearsome, giant lizards doesn’t mean they had to bask to raise their body temperature. After all, birds, likely their lone surviving descendants, are warm-blooded.

Researchers have looked at this question from many different angles (including temperature measurements from teeth, as we reported last year). One intriguing line of evidence has come from the microscale structure of their bones. Cross sections through fossils from most groups of dinosaurs (except sauropods) reveal cycles in growth, including dark lines where growth temporarily ceased.

This has long been cited as strong evidence in favor of cold-bloodedness, as the bones of modern cold-blooded species also show annual cycles. Since their body temperature is at the whim of the seasons, their growth slows during non-ideal conditions. Warm-blooded animals, on the other hand, keep their body temperature constant, and so their bone growth, too, remains constant. Or so the story went.

Some argued that the dinosaur bones actually showed signs of very high rates of growth in between the cyclical lulls. The high metabolism required to do so is more characteristic of warm-blooded animals, they said. But the cold-blooded camp maintained that only cold-blooded animals showed the alternating growth patterns.

As it turns out, that well-ordered house was built on sand. The evidence for constant bone growth in warm-blooded organisms was lacking. A paper published in the journal Nature describes a large review of ruminants (mammals that chew cud) and comes to the opposite conclusion—dinosaur bone growth looks more like warm-blooded organisms than cold-blooded ones.

The researchers examined femurs from over 100 African and European ruminants spanning climate zones from the tropics to the arctic. They found patterns of high bone growth rates that correlated with the growing season and hiatuses in growth during the dry or cold season.

To dig into the mechanisms driving this pattern, they used physiological data collected from Svalbard reindeer and alpine red deer. These studies measured changes in things like hormones and body temperature throughout the year.

The data showed that these species save energy by slowing their metabolism (and growth) when food is scarce, even reducing body temperature by a small amount (less than 1°C). During the best part of the growing season, metabolic activity kicks into high gear. The progress comes in tying that physiological strategy to the fine-scale bone structure, and showing that it’s pervasive across such a large group of warm-blooded animals.

The researchers argue this work not only "debunks the key argument from bone histology in support of" cold-bloodedness, it also corrals the bone patterns under the umbrella of evidence for warm-bloodedness. They think there’s a good chance that dinosaurs had similar metabolic schemes as these modern ruminants, staying in tune with the seasonal availability of food.

We’ll see if the rest of the paleontology community agrees. Odds are, some will have a bone to pick.

If you insist on the term "warm-blooded" you won't see the sauropod legs for all the bone rings. This colloquial term seems to have been replaced the last 3 decades by terms that describes different aspects of thermoregulation:

"Both the terms "warm-blooded" and "cold-blooded" have fallen out of favour with scientists because of the vagueness of the terms and an increased understanding of the field. Body temperature types are not discrete categories. Each term may be replaced with one or more variants (see the next section for examples). Body temperature maintenance (thermoregulation) incorporates a wide range of different techniques that result in a body temperature continuum."

"A large proportion of the creatures traditionally called "warm-blooded", such as mammals and birds, fit all three of these categories. However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many bats and small birds are poikilothermic and bradymetabolic when they sleep for the night, or day, as the case may be. For these creatures, the term heterothermy was coined."

A paper published in the journal Nature describes a large review of ruminants (mammals that chew cud)

Why not avians? You know, since they're related to dinosaurs more directly. Also, what's the state of knowledge on the DNA behind avian warm-bloodedness? Can't comparative studies let them "turn back the genetic clock" as they always say on TV specials?

A paper published in the journal Nature describes a large review of ruminants (mammals that chew cud)

Why not avians? You know, since they're related to dinosaurs more directly. Also, what's the state of knowledge on the DNA behind avian warm-bloodedness? Can't comparative studies let them "turn back the genetic clock" as they always say on TV specials?

Not an anatomy expert, but as far as I know the avian bones have adapted to flight in the time post avian-dinosaur divergence. They are hollow, thin, light weight and so forth. Thus I would assume that the growth patterns are also quite different.

A paper published in the journal Nature describes a large review of ruminants (mammals that chew cud)

Why not avians? You know, since they're related to dinosaurs more directly. Also, what's the state of knowledge on the DNA behind avian warm-bloodedness? Can't comparative studies let them "turn back the genetic clock" as they always say on TV specials?

Not an anatomy expert, but as far as I know the avian bones have adapted to flight in the time post avian-dinosaur divergence. They are hollow, thin, light weight and so forth. Thus I would assume that the growth patterns are also quite different.

These are good points, but we also have flightless birds (emu, ostrich) which might be valuable comparisons.

Yeah I didn't think was still in question. From school, and general knowledge of how things work I thought that Dino's were a mix of hot/cold blooded.

I thought that if a dino had fat build up beneth the skin, to facilitate insulation they were warm blooded. While dino's with out fat build up were cold blooded.

If they don't have fat for insulation, like birds with feathers then still warm blooded. Basically if there is no external or internal forms of epidermus insulation they are cold blooded.

I see that you were fed a load of crap in school.

The dinosaur line started out as a small creature in an already established biofauna that was already Endothermic (protomammals etc) and very quickly out competed and diversified to a degree that they dominated for over 130million years during which time they actively suppressed anything larger than a cat from developing.

Since they all come from a single beginning its preposterous to claim that some of the descendants lost the advantage of being Endothermic and instead devolving into Exothermic state.

Besides you cant possibly mean that the heat isolation feature of a specie determines if it creates it own body heat or not?

If then I do understand why some still cling to the

Quote:

"okay small dinos might be hot blooded BUT brontosaurs dinos was coldblooded, they were so big they didn't get cold"

Yeah I didn't think was still in question. From school, and general knowledge of how things work I thought that Dino's were a mix of hot/cold blooded.

I thought that if a dino had fat build up beneth the skin, to facilitate insulation they were warm blooded. While dino's with out fat build up were cold blooded.

If they don't have fat for insulation, like birds with feathers then still warm blooded. Basically if there is no external or internal forms of epidermus insulation they are cold blooded.

I see that you were fed a load of crap in school.

The dinosaur line started out as a small creature in an already established biofauna that was already Endothermic (protomammals etc) and very quickly out competed and diversified to a degree that they dominated for over 130million years during which time they actively suppressed anything larger than a cat from developing.

Since they all come from a single beginning its preposterous to claim that some of the descendants lost the advantage of being Endothermic and instead devolving into Exothermic state.

Besides you cant possibly mean that the heat isolation feature of a specie determines if it creates it own body heat or not?

If then I do understand why some still cling to the

Quote:

"okay small dinos might be hot blooded BUT brontosaurs dinos was coldblooded, they were so big they didn't get cold"

insanity.

You sir are being an arse hole. Reign in your self righteous emotions and get over your self.

As for the statement that Endothermic > Exothermic. Well that clearly shows you like pulling things out of your arse. I'll think you'll find that there are merits to both and which one wins depends on your arguments context.

Why not avians? You know, since they're related to dinosaurs more directly.

They just started to look at these effects. And according to the article they wanted to have a large group of large animals (for easy comparison) with large differential growth: "The progress comes in tying that physiological strategy to the fine-scale bone structure, and showing that it’s pervasive across such a large group".

Who knows how far they can take it?

MoonShark wrote:

Also, what's the state of knowledge on the DNA behind avian warm-bloodedness? Can't comparative studies let them "turn back the genetic clock" as they always say on TV specials?

It seems to be a complex trait, see the physiological mechanisms for metabolic and growth rates mentioned in the article. If body length is controlled by 1000s of genes, growth will be too. Metabolism is certainly finely regulated.

So, an informed guess would be that it is too complex as of yet.

Technoid.se wrote:

The dinosaur line started out as a small creature in an already established biofauna that was already Endothermic (protomammals etc) and very quickly out competed and diversified to a degree that they dominated for over 130million years during which time they actively suppressed anything larger than a cat from developing.

Since they all come from a single beginning its preposterous to claim that some of the descendants lost the advantage of being Endothermic and instead devolving into Exothermic state.

Extant reptiles are not endothermic in general, so it evolved independently yet again. Then mammals and birds in general evolved it independently - diapsids includes crocodiles, lizards, snakes, and tuatara, as well as dinosaurs - synapsids, who includes mammals, are another clade. [Wikipedia]

But see my first comment on heterotherms; some lost the capability again.

The question they are looking for is how far back generic dinosaur endothermy, or as here homeothermy, goes. (I don't think they can tell on endothermy, only homeothermy.)

What *is* preposterous is to see the term "devolving". Traits are successful or not, there is no other comparison to be made, say of aesthetic value.* Hence biologists never say 'devolved' - the process is evolution, and so populations evolve. Always.

----------------------* Sometimes you can see the value term "simplification", since loosing many traits may make for a simpler organism in terms of complexity - number of parts and how they relate. The best example is of course parasitic simplification, all known parasites are simpler than their ancestors as far as I know.

Incidentally parasites are the most successful complex multicellular organisms, more than 50 % of species are parasites. Hence simplification is a most successful way of adapting to the most successful way of life.

On that note, while I haven't read "Parasite Rex" by Carl Zimmer, I am fairly sure he takes us through that and adds that parasites is the most powerful evolutionary force for complex multicellular life. It forms our immune system with its many traits, and interaction with parasites is legion.

The idea of a "crown of species" from the medieval religious "ladder of life" goes not to humans but to the parasites, they ownz.

Anders, I read it to mean that he wasn't sure how these traits and species relate. Homeothermy can evolve independently, and anyway you can always question whether deeper relationships have any descendants or if you have a split. (Taxonomical vs cladistic lineages - are birds descendants of reptiles, fishes et cetera? Taxonomically no, cladistically yes.)

But for now, the hypothesis is (as I take it) that it started somewhere closer before birds and perhaps related to use of feathers for insulation. (Which use is another box of iffy.)

What about the relationship between dinosaurs and crocodilia (crocs, the non-crappy-shoeware variety, and alligators)? I thought they and birds were offshoots of the same ancestor, Archosaur?

"Archosaur" isn't an ancestor, it's a classification. Dinosaurs and crocodiles are both archosaurs, but neither one is descended from the other (here's a nice cladogram). Birds are just a subset of dinosaurs. To look at the fossil record, there was a time up to the late Triassic where large, fast, active, land-dwelling crocodilians competed with dinosaurs for the top spot on the food chain. They tended to have underslung legs and might have been endothermic (imagine a scaly greyhound with a crocodile's head and tail, loping along towards you. Pretty freaky). Modern crocodilians have their own take on a four-chambered heart, something that's characteristic of endothermic animals; it might be left over from a "warm-blooded" ancestry that was lost over time, possibly because all remaining crocs are aquatic. They may have developed ectothermy as a way to adapt to life in the water, despite originally being endothermic.

Yeah I didn't think was still in question. From school, and general knowledge of how things work I thought that Dino's were a mix of hot/cold blooded.

I thought that if a dino had fat build up beneth the skin, to facilitate insulation they were warm blooded. While dino's with out fat build up were cold blooded.

If they don't have fat for insulation, like birds with feathers then still warm blooded. Basically if there is no external or internal forms of epidermus insulation they are cold blooded.

I see that you were fed a load of crap in school.

The dinosaur line started out as a small creature in an already established biofauna that was already Endothermic (protomammals etc) and very quickly out competed and diversified to a degree that they dominated for over 130million years during which time they actively suppressed anything larger than a cat from developing.

Since they all come from a single beginning its preposterous to claim that some of the descendants lost the advantage of being Endothermic and instead devolving into Exothermic state.

Besides you cant possibly mean that the heat isolation feature of a specie determines if it creates it own body heat or not?

If then I do understand why some still cling to the

Quote:

"okay small dinos might be hot blooded BUT brontosaurs dinos was coldblooded, they were so big they didn't get cold"

insanity.

You sir are being an arse hole. Reign in your self righteous emotions and get over your self.

Well, if you say so, Okay.

Wellard wrote:

As for the statement that Endothermic > Exothermic. Well that clearly shows you like pulling things out of your arse. I'll think you'll find that there are merits to both and which one wins depends on your arguments context.

In the context of the situation where the dinosaurs dominated and suppressed other species being Endothermic is better than being Exothermic.This is stuff I read and I thought sounded logical which I here repeat and being an arsehole I don't cite my sources

Torbjörn Larsson, OM wrote:

Technoid.se wrote:

The dinosaur line started out as a small creature in an already established biofauna that was already Endothermic (protomammals etc) and very quickly out competed and diversified to a degree that they dominated for over 130million years during which time they actively suppressed anything larger than a cat from developing.

Since they all come from a single beginning its preposterous to claim that some of the descendants lost the advantage of being Endothermic and instead devolving into Exothermic state.

Extant reptiles are not endothermic in general, so it evolved independently yet again. Then mammals and birds in general evolved it independently - diapsids includes crocodiles, lizards, snakes, and tuatara, as well as dinosaurs - synapsids, who includes mammals, are another clade. [Wikipedia]

But see my first comment on heterotherms; some lost the capability again.

Rather disabled due to environmental factors from your examples so I disagree that they have "lost it".(besides does that mean bears in hibernation also loses it?)

Torbjörn Larsson, OM wrote:

The question they are looking for is how far back generic dinosaur endothermy, or as here homeothermy, goes. (I don't think they can tell on endothermy, only homeothermy.)

What *is* preposterous is to see the term "devolving". Traits are successful or not, there is no other comparison to be made, say of aesthetic value.* Hence biologists never say 'devolved' - the process is evolution, and so populations evolve. Always.

you are right that was a poor choice of word, I'll avoid it in the future, happy?